A press of the afore-mentioned kind, in which the stroke stop is configured as a return stroke stop, is disclosed in DE 199 59 627 A1.
Manually operated presses of the type described above are conventionally used at piece-work workplaces. As the force to be exerted during a manual actuation of the press increases when the stroke end position is approached, some workers tend to effect the pressing operation only incompletely and to initiate the return stroke already ahead of the intended lower end position of the pressing stroke. However, the pressing operation is then not completed correctly so that workpieces of minor quality are generated or even scrap.
In order to counteract these problems, on has equipped manually operated presses with a so-called return stroke stop. In conventional manually operated presses the return stroke stop is configured mechanically. In the above-mentioned prior art press the mechanical return stroke stop is configured by means of a grooved disk together with a latching pin. When a manual lever is actuated, the grooved disk is rotated and the latching pin runs along a predetermined groove track of the grooved disk. At two positions corresponding to the end of the coarse stroke and the beginning of the fine stroke, resp., the groove track is provided with steps. As soon as the latching pin has jumped over a step, the grooved disk may no more be rotated rearwardly over such step, i.e. the press ram may no more be displaced back upwardly. Only when the press ram has run through the entire press stroke, the latching pin assumes a position in which it may automatically return to the beginning of the groove track. Accordingly, the press ram may only be displaced again upwardly into its initial position, when the press ram has entirely run through its stroke.
Although the concept described before has been well approved in practice, further improvements are desired under various aspects.
To begin with, a first problem exists in that conventional pressing operations are not adapted to be documented, in contrast to automatically effected pressing operations in which numerically controlled pneumatic presses are conventionally used. In many fields of application this is no more acceptable, in particular when production processes shall be certified according to the ISO 9000 standard.
A second problem with manually operated presses of the type specified at the outset consists in that an individual grooved disk has to be manufactured for each pressing operation. This is because the length of the coarse stroke and the length of the fine stroke individually depend on the particular workpiece to be joined. All that has a negative impact on so-called sequential multiple pressings. In such working operations a plurality of items are joined together one after the other in a sequence of pressing sub-operations, for example a Seeger circlip ring, a bearing, a pinion, a gasket etc. are joined onto a shaft one after the other.
Conventionally, one has effected such multiple pressings by effecting the individual sub-operations one after the other at different workplaces. As a consequence, as many workers were required as individual pressing sub-operations had to be effected.
Finally, a third problem exists with conventional manually operated presses of the type specified at the outset, to ensure that so-called good workpieces are distinguished from so-called bad workpieces. In this context, it has been known, for example from DE 197 05 462 A1, to equip a press with a first sensor for detecting the press stroke travel and with a second sensor for detecting the pressing force, and to generate a travel vs. force diagram for each pressing operation being indicative for a good or a bad pressing operation, resp. Namely, if the measured travel vs. force curve is within a predetermined tolerance band, the particular workpiece is determined to be well pressed, i.e. to be a good workpiece. In the alternative, the workpiece is determined to be a bad workpiece, i.e. to be scrap which has to be disposed of.
With automatic presses having a pneumatic drive, it is known in this context to switch the press off when a bad workpiece is detected, the switching off being effected when the bad workpiece is still within the press. The reason for this measure is to prevent the worker from simply continuing his work after a bad workpiece was detected. Instead, the worker has to call for his foreman or master who puts the press back into operation, for example by actuating a key operated switch with a special key. For putting the press back into operation it is, however, mandatory to remove the bad workpiece beforehand. Considering that this procedure generates a lot of attention, it may be assumed that the bad workpiece, after having been removed from the press, is transferred into a special bad workpiece container and is eliminated from the further process.
Finally, there are situations in which one wants to prevent that the press ram may be displaced beyond a predetermined stroke position during the working stroke, wherein it should be possible to determine this position depending on the particular process.
It is an object underlying the invention to further improve a manually operated press such that the above-mentioned problems are avoided. In particular, a manually operated press shall be provided, in which the pressing operations may be documented, in which multiple pressings may be effected in a simple manner and without the need of making mechanical modifications, and, finally having the option to provide for means guaranteeing the elimination of bad workpieces with a high probability.